Optical links provide high data transmission rates at low power, and thus present a solution for replacing ordinary copper interconnects between integrated circuits. Optical reception is based on capturing, using a photosensitive device such as a photodiode, a light signal that is generally encoded in a digital fashion, and which may have a power level as low as 10 μW. The photosensitive device for example generates a small current that is transformed by the optical receiver into a digital voltage signal.
In order to correctly receive a data signal transmitted optically over such an optical link, it is generally necessary to receive a timing signal over the optical link. In some embodiments, the timing signal may be extracted from the data signal itself, but such solutions tend to be complex to implement. Indeed, the data encoding will generally mean that a timing edge is not present in the data signal for each data bit of the data transmitted over the link.
Alternative solutions use a separate clock channel for transmitting a clock signal. In order to reduce power consumption, it has been proposed to transmit the clock signal over the optical link as a series of pulses rather than as a clock signal having a 50% duty cycle. For example, such a technique is described in the publication by A. Bhatnagar et al. entitled “Receiverless detection schemes for optical clock distribution”, Proceedings of the SPIE—The International Society for Optical Engineering, 6 Jul. 2004, vol. 5359, no. 1, p. 352-9. According to the technique described in this publication, the optical clock signal is transmitted as two sequences of pulses, each of which is received by a corresponding photodiode and converted into a voltage signal. However, a high level of charge is required to charge the parasitic capacitances of the two photodiodes and trigger the detection by a voltage amplifier. Furthermore, the two photodiodes lead to a relatively large footprint of the circuit.
There is thus a need in the art for an optical receiver suitable for receiving a low power optical signal and having reduced power consumption and/or reduced surface area with respect to existing solutions.